Bug#140155: marked as done (libc6: printf() + shared memory = race condition)
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and subject line dont use clone with printk
has caused the attached Bug report to be marked as done.
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From: Johan Walles <johan@appeal.se>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: libc6: printf() + shared memory = race condition
X-Mailer: reportbug 1.48
Date: Wed, 27 Mar 2002 15:12:44 +0100
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Package: libc6
Version: 2.2.5-3
Severity: normal
Run the below program a couple of times. Roughly half of the times
one of the lines is printed twice, or some characters aren't printed
at all. I have tried it on three separate machines; this single CPU
x86 Debian Testing one, a 2 CPU x86 with RH7.1, and another single CPU
x86 with RH6.2. All three machines have similar problems.
According to the libc info page about "Streams and Threads", "issuing
two stream operations for the same stream in two threads at the same
time will cause the operations to be executed as if they were issued
sequentially.". For me, that is obviously not the case.
I also have problems with crashes when using clone() and printf()
together that may be related to this, but I'll report that separately
when I can provoke it with a short example program.
"
#include <stdio.h>
#include <sched.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/types.h>
int childfunc(void *arg)
{
assert(printf("Child %d: Hello\n", getpid()) >= 0);
assert(printf("Child %d: Good bye\n", getpid()) >= 0);
return 0;
}
int main(int argc, char *argv[])
{
const size_t stacksize = 65536;
pid_t cloneResult;
int cloneErrno;
void *stack = malloc(stacksize);
cloneResult = clone(childfunc,
stack + stacksize,
CLONE_VM| CLONE_FILES,
(void *)0xDeadf00d);
cloneErrno = errno;
if (cloneResult <= 0) {
perror("Clone() failed");
exit(EXIT_FAILURE);
}
assert(printf("Parent %d: This is a random printout\n", getpid()) >= 0);
return 0;
}
"
-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux barbara 2.4.16-686 #1 Wed Nov 28 09:27:17 EST 2001 i686
Locale: LANG=sv_SE.ISO-8859-1, LC_CTYPE=sv_SE.ISO-8859-1
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>From herbert@gondor.apana.org.au Sat Aug 24 08:20:44 2002
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Date: Sat, 24 Aug 2002 23:20:38 +1000
To: 140155-done@bugs.debian.org
Subject: dont use clone with printk
Message-ID: <20020824132038.GA31463@gondor.apana.org.au>
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From: Herbert Xu <herbert@gondor.apana.org.au>
Delivered-To: 140155-done@bugs.debian.org
Using printk with a direct clone leads to undefined behaviour.
--
Debian GNU/Linux 3.0 is out! ( http://www.debian.org/ )
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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